The present invention relates in general to the preservation of blood and, in particular, to a new and useful method and apparatus for storing and preparing cryopreserved blood particularly red blood cells.
The supply, storage and use of blood or components thereof poses various and long standing problems in the field of medicine. While large quantities of blood or its components are always in demand, the requirements are sporadic and unpredictable so that large quantities must be stored and maintained at various locations such as blood banks and large hospitals. While such quantities must always be maintained and held ready, a standing problem exists particularly with the storage of red blood cells, in that the red blood cells and other blood components are highly perishable. One very important solution in preserving blood has been the development of techniques in freezing red blood cells or whole blood to preserve them for long periods of time. To prevent the destruction of the red blood cells while they are being frozen, it has been found necessary to add a cryopreserving agent to the blood. When the blood is to be used, after it has been thawed, this cryopreserving agent must be washed out of the blood. The usual agent used is glycerol at a concentration of between about 40 to 50%. With the use of such high amounts of glycerol, the rate of freezing or thawing has not been found to be critical and storage of the blood or red blood cells is at between -60.degree. C. to -80.degree. C. Storage can be in liquid nitrogen, liquid nitrogen vapor or achieved by mechanical refrigeration devices or dry ice. The blood has been found to be stable even with rises in the storage temperature so that the so preserved blood can be transported in dry ice to areas of consumption.
While the blood stored in high concentrations of glycerol is relatively insensitive to temperature changes, the concentration of glycerol itself has posed a problem in that it must be somehow removed before the blood is used. In one example, it has been found necessary to use no less than seven dilution and sedimentation cycles over a period of hours in order to remove the glycerol from the blood or red blood cells which have been frozen in 40% glycerol. This process known as deglycerolization, was improved somewhat by the introduction of an agglomeration process by which the red blood cells could be sedimented without the use of a centrifuge device.
An improvement in the above method of freezing blood or red blood cells came with the introduction of a technique using relatively low concentrations of glycerol. It was found that the concentration of glycerol could be reduced to approximately 20% which permitted deglycerolization in three or four sedimentation cycles in a clinical centrifuge with the process time reduced to one or two hours. The reduction in glycerol concentration, however increased the sensitivity of the blood to temperature changes so that the blood preserved by this method required storage and transportation in liquid nitrogen or liquid nitrogen vapor. It was found that even transient rises in the storage temperature led to extreme hemolysis of the red blood cells.
Some of the problems outlined above in removing the cryoprotective agent from the blood have been solved by the introduction and use of cell washing devices which are capable of automatically processing large quantities of blood. The cost of such units is high, however, and is only economical when large quantities of blood are available to be processed.
Additional problems in removing the cryopreserving agent from frozen blood or red blood cells is the possible introduction of contaminants since, at some point in the known processes, the blood is brought into direct contact with washing solutions and the like which must be supplied from some source external to the container in which the blood was collected and stored. Another problem in using frozen blood is the relatively long time period which is required to render the blood usable, that is deglycerolized. Especially when the blood is used in small institutions such as hospitals located at remote areas, an emergency situation requiring unexpected large quantities of blood cannot be treated effectively since the time lag required in processing the frozen blood would be prohibitive. Another problem existing where emergencies are anticipated and large quantities of blood are prepared is that the frozen blood once thawed and deglycerolized has a life of only about 24 hours. If for some reason the emergency fails to materialize, the blood must either be used elsewhere within the 24 hours or else it is outdated and no longer useful. It must also be noted that the blood must be matched to potential donors so that this reduces further the number of potential recipients which can use the thawed blood. This loss of otherwise useful blood is particularly onerous in view of the difficulty in obtaining and maintaining sufficient blood supplies throughout the United States. The discovery and use of a technique of thawing and deglycerolizing frozen bood or red blood cells in a relatively short period of time would be particularly useful not only in permitting the emergency use of frozen blood but would also enhance the inventory control of blood since frozen blood can be stockpiled in periods of high availability and then selectively used in periods of shortage.